This application is a national stage application of PCI/DE98/02209, filed Jul. 29, 1998.
The present invention relates to a method and a mold for producing an umbrella-type insulator made of plastic material, having a core constructed as a solid body and having umbrellas connected with the core as well as having collars which are molded to the umbrellas and coaxially surround the core, by a mold which reaches coaxially around the core and forms a ring gap with respect to the core at the collar end of the respective umbrella to be molded. The ring gap being sealed off by means of an elastic seal, and wherein after sealing off, a first pourable material, which cross-links with the core to form a firm electrically insulating body, is poured into the mold and after the cross-linkage and the formation of the respective umbrella with the collar, the mold with the seal is moved away from the umbrella and in the process, the formed umbrella with the collar is removed from the mold.
An umbrella-type insulator of this type is known from German Patent Document DE-A-23 00 145. It consists of a core and of several umbrellas which are molded to the core and have one downward-extending collar respectively molded to the umbrellas and connected with the core. The production takes place such that first a two-part mold, which is tightly pressed together, is placed over the core and forms a funnel-shaped casting mold; during the pouring-in of the insulating material, the conical portion of the casting mold forming the umbrella and its lower portion forming the collar. On the bottom, the mold surrounds the core at a distance in the form of a ring gap which is sealed off before the casting process by a sealing ring. After the solidification of the insulating material, the mold parts are laterally taken off.
In tests with a single-part or multi-part casting mold which, after the solidification of the insulating or casting material, is pulled away in the downward direction, it was found that, when the umbrella is removed from the mold by pulling away the mold in the downward direction, the umbrella is occasionally also pulled away downward and the edge of the umbrella is deformed to such an extent, that is, bent downward, that tensions or even cracks occur in the umbrella material. As the result, a perfect insulation will no longer be ensured.
It is an object of the present invention to provide a method and a mold by means of which it is possible to achieve a perfect removal of the umbrellas from the mold.
This object is achieved by utilizing a mold which has at least one laterally arranged valve which extends to a surface of one of the umbrella and the collar coaxially around the core; pouring a material into the mold which cross-links with the core to form the insulating body comprising a core, collar and umbrella; begin axial moving-away of the mold from the umbrella and collar resulting in a vacuum forming between the mold and the formed insulating body; and then opening the valve and allowing a gaseous medium to be introduced into a cavity formed between the insulator and the mold so that the pulling-away of the mold is permitted without any unacceptable deformation of the umbrella.
By means of these measures and characteristics according to the invention, the umbrella can no longer adhere to the mold during the removal from the mold because a vacuum forms between the mold and the umbrella only for a short time or not at all. The umbrella can therefore be removed from the mold without any deformation.